The present invention relates to a novel stabilizer mixture which markedly slows the metal-compound-accelerated degradation and aging of organic materials, in particular of organic polymers.
There is a wide variety of ways by which organic materials, in particular plastics, can come into contact with metals, metal ions and metal-containing compounds. Contact of this type is impossible to avoid particularly in cases of residues of metallic catalysts used to prepare the plastic. There are also many ways in which organic polymers during their processing come into contact with metallic surfaces. In addition, various metal-containing compounds are intentionally admixed with the plastic to achieve specific effects: examples of these are metal-containing stabilizers, pigments and fillers. In addition, organic polymers are very frequently in direct contact with metals in end applications, as is often the case with cable sheathings, pipes and electronic components.
Like all organic compounds, plastics too are subject to natural aging. This process, which is associated with impairment of functional properties and always ends with the decomposition of the organic material, can be accelerated by accelerators and slowed by stabilizers. Metals and metal-containing compounds are generally known to be accelerators for degradation and ageing processes of this type (cf. R. Gachter, H. Muller, Taschenbuch der Kunststoff-Additive [Plastics Additives Handbook], Carl Hanser Verlag Munich, Vienna; 3rd edn. 1989; Chapter 2, pp. 109 ff).
The use of a condensation product made from phosphorus trichloride (1) and 2,2'-dimethyl-4,4'-dihydroxy-5,5'-di-tert-butyidiphenyl sulfide (2) in a mixture with other chemicals is described in DE-A-1 153 894. However, there is no indication of a stabilizing action of the product on its own. This condensation product is used in this document only in combination with the condensation product made from nonylphenol and acetone and with dilauryl thiodipropionate (Comparative Experiment No. 5). DE-A-1 153 894 describes the stabilizing action of the mixture described against the damaging action of heat and oxygen on copper-contaminated polypropylene.
The effectiveness of a condensation product made from (1) and (2) alone and its use as a stabilizer for organic material had not been described until the publication of DE-A-3 029 176. The compound described there is a three-dimensionally crosslinked polymer insoluble in all organic solvents and having a phosphorus content of 4.9% (DE-A-3 029 176, p. 2, line 17; p. 5, Example 3). This document describes the stabilizing action of the high-molecular-weight, insoluble condensation product, with a degree of polymerization of from 50 to 500, on a polymer (p. 3, line 45). Stabilization against the damaging actions of oxygen and heat is described. The starting materials (1) and (2) used there are brought together to prepare the condensation product within a period of 15 min at only 50.degree. C. in xylene in the presence of a small amount of dimethylformamide, after stirring (50.degree. C.) for 1 hour are heated to 135.degree. C. and condensed at this temperature for 1 hour with elimination of hydrogen chloride.
The condensation product known from the prior art is insoluble in organic solvents and has unsatisfactory stabilizing action. The object was therefore to provide a product which has better solubility and is more effective.